New techniques, such as digital simulations of an original sound field using a dummy head(microphone)and these applications to room acoustics are being work on, but have not yet reached a stage of practical usefulness. A modified version of the equalizing network on a dummy head system for free-field reproduction with two loudspeakers, in a network configured as a bubble memory and a microcomputer controlled digital arithmetic system is presented in this paper. This dummy head system using the equalizing network will be referred to as Orthostereophonic System(OSS). The equalizing network can be applied to an asymmetric condition of head-related transfer functions(HRTF), and is found to be particularly useful in the hardware construction method or accurate simulation of an original sound field using digital system. In order to improve the precision of prefiltering, a mixed phase nature of HRTF is discussed from a standpoint of inverse filtering. Then, a digital equalizer utilizing finite impulse response(FIR)digital filters is developed with taking care to the phase characteristic including all-pass phase. The physical performance of the equalizing network was evaluated with a newly defined testing procedure(Orthostereophonic response-network(OSRN))which has demonstrated the effects of design parameters(impule response duration, quantization bit length, Smoothing processing etc. )of the FIR digital filters.
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